Editing C. V. Raman (section)

=== Blue color of the sea ===

Raman, in his broadening venture on optics, started to investigate scattering of light starting in 1919.<ref>{{Cite journal|last=Raman|first=C.V.|date=1919|title=LVI. The scattering of light in the refractive media of the eye|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|language=en|volume=38|issue=227|pages=568–572|doi=10.1080/14786441108635985|url=https://zenodo.org/record/1554442|access-date=10 March 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031081718/https://zenodo.org/record/1554442|url-status=live}}</ref> His first phenomenal discovery of the physics of light was the [[Color of water|blue color of seawater]]. During a voyage home from England on board the ''S.S. Narkunda'' in September 1921, he contemplated the blue color of the [[Mediterranean Sea]]. Using simple optical equipment, a pocket-sized [[spectroscope]] and a [[Nicol prism]] in hand, he studied the sea water.<ref>{{Cite journal|last=Anon.|date=2009|title=This Month in Physics History: February 1928: Raman scattering discovered|url=https://www.aps.org/publications/apsnews/200902/physicshistory.cfm|journal=APS News|volume=12|issue=2|pages=online|access-date=10 March 2020|archive-date=6 March 2020|archive-url=https://web.archive.org/web/20200306100800/https://www.aps.org/publications/apsnews/200902/physicshistory.cfm|url-status=live}}</ref> Of several hypotheses on the colour of the sea propounded at the time,<ref>{{Cite journal|last=Buchanan|first=J. Y.|date=1910|title=Colour of the Sea|journal=Nature|language=en|volume=84|issue=2125|pages=87–89|doi=10.1038/084087a0|bibcode=1910Natur..84...87B|doi-access=free}}</ref><ref>{{Cite journal|last=Barnes|first=H. T.|date=1910|title=Colour of Water and Ice|journal=Nature|language=en|volume=83|issue=2111|pages=188|doi=10.1038/083188a0|bibcode=1910Natur..83..188B|s2cid=3943242|url=https://zenodo.org/record/1567754|doi-access=free|access-date=16 March 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031080914/https://zenodo.org/record/1567754|url-status=live}}</ref> the best explanation had been that of [[Lord Rayleigh]]'s in 1910, according to which, "The much admired dark blue of the deep sea has nothing to do with the color of water, but is simply the blue of the sky seen by reflection".<ref>{{Cite journal|last=Rayleigh|first=J.W.S.|date=1910|title=Colours of Sea and Sky|journal=Nature|language=en|volume=83|issue=2106|pages=48–50|doi=10.1038/083048a0|bibcode=1910Natur..83...48.|doi-access=free}}</ref> Rayleigh had correctly described the nature of the blue sky by a phenomenon now known as [[Rayleigh scattering]],<ref>{{Cite journal|last=Rayleigh|first=Lord|date=1899|title=XXXIV. On the transmission of light through an atmosphere containing small particles in suspension, and on the origin of the blue of the sky|url=https://zenodo.org/record/1431249|url-status=live|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|language=en|volume=47|issue=287|pages=375–384|doi=10.1080/14786449908621276|archive-url=https://web.archive.org/web/20201031200404/https://zenodo.org/record/1431249|archive-date=31 October 2020|access-date=16 March 2020}}</ref> the scattering of light and refraction by particles in the atmosphere.<ref>{{Cite journal|last1=Stetefeld|first1=Jörg|last2=McKenna|first2=Sean A.|last3=Patel|first3=Trushar R.|date=2016|title=Dynamic light scattering: a practical guide and applications in biomedical sciences|journal=Biophysical Reviews|language=en|volume=8|issue=4|pages=409–427|doi=10.1007/s12551-016-0218-6|pmc=5425802|pmid=28510011}}</ref> His explanation of the blue colour of water was instinctively accepted as correct. Raman could view the water using a [[Nicol prism]] to avoid the influence of sunlight reflected by the surface. He described how the sea appears even more blue than usual, contradicting Rayleigh.<ref name="Nature1921">{{Cite journal|last=Raman|first=C. V.|date=1921|title=The Colour of the Sea|journal=Nature|language=en|volume=108|issue=2716|pages=367|doi=10.1038/108367a0|bibcode=1921Natur.108..367R|s2cid=4064467|doi-access=free}}</ref>

As soon as the ''S.S. Narkunda'' docked in Bombay Harbour (now [[Mumbai Harbour]]), Raman finished an article "The colour of the sea" that was published in the November 1921 issue of ''Nature''. He noted that Rayleigh's explanation is "questionable by a simple mode of observation" (using Nicol prism).<ref name="Nature1921" /> As he thought:{{blockquote|

Looking down into the water with a Nicol in front of the eye to cut off surface reflections, the track of the sun's rays could be seen entering the water and appearing by virtue of perspective to converge to a point at a considerable depth inside it. The question is: What is it that diffracts the light and makes its passage visible? An interesting possibility that should be considered in this connection is that the diffracting particles may, at least in part, be the molecules of the water themselves.<ref name="Mukherji-2018b" />}}
[[File:Raman-2.jpg|alt=Title page to Raman's Molecular Diffraction of Light (1922)|thumb|230x230px|Title page to Raman's ''Molecular Diffraction of Light'' (1922)]]

When he reached Calcutta, he asked his student K. R. Ramanathan, who was from the University of Rangoon, to conduct further research at IACS.<ref name="Mallik-2000">{{Cite journal|last=Mallik|first=D. C. V.|date=2000|title=The Raman Effect and Krishnan's Diary|journal=Notes and Records of the Royal Society of London|volume=54|issue=1|pages=67–83|jstor=532059|doi=10.1098/rsnr.2000.0097|s2cid=143485844}}</ref> By early 1922, Raman came to a conclusion, as he reported in the ''[[Proceedings of the Royal Society of London]]'':{{blockquote|It is proposed in this paper to urge an entirely different view, that in this phenomenon, as in the parallel case of the colour of the sky, ''molecular diffraction'' determines the observed luminosity and in great measure also its colour. As a necessary preliminary to the discussion, a theoretical calculation and experimental observations of the intensity of molecular scattering in water will be presented.<ref>{{Cite journal|last=Raman|first=C.V.|date=1922|title=On the molecular scattering of light in water and the colour of the sea|journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character|language=en|volume=101|issue=708|pages=64–80|doi=10.1098/rspa.1922.0025|bibcode=1922RSPSA.101...64R|doi-access=free}}</ref>}}True to his words, Ramanathan published an elaborate experimental finding in 1923.<ref>{{Cite journal|last=Ramanathan|first=K.R.|date=1923|title=LVIII. On the colour of the sea|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|language=en|volume=46|issue=273|pages=543–553|doi=10.1080/14786442308634277}}</ref> His subsequent study of the [[Bay of Bengal]] in 1924 provided the full evidence.<ref>{{Cite journal|last=Ramanathan|first=K. R.|date=1 March 1925|title=The Transparency and Color of the Sea|journal=Physical Review|language=en|volume=25|issue=3|pages=386–390|doi=10.1103/PhysRev.25.386|bibcode=1925PhRv...25..386R}}</ref> It is now known that the intrinsic color of water is mainly attributed to the selective absorption of longer wavelengths of light in the red and orange regions of the [[spectrum]], owing to overtones of the [[infrared]] absorbing O-H (oxygen and hydrogen combined) stretching modes of water molecules.<ref name="Braun">{{Citation|last1=Braun|first1=Charles L.|title=Why is water blue?|url=http://inside.mines.edu/fs_home/dwu/classes/CH353/study/Why%20is%20Water%20Blue.pdf|journal=[[Journal of Chemical Education]]|volume=70|issue=8|pages=612–614|year=1993|bibcode=1993JChEd..70..612B|doi=10.1021/ed070p612|last2=Smirnov|first2=Sergei N.|access-date=27 July 2021|archive-date=1 December 2019|archive-url=https://web.archive.org/web/20191201000418/http://inside.mines.edu/fs_home/dwu/classes/CH353/study/Why%20is%20Water%20Blue.pdf|url-status=live}}</ref>